Magnetic voltage reference



y 1952 J. D. WELCH 3,036,262

' MAGNETIC VOLTAGE REFERENCE Filed May 19, 1958 It? I? E OUT INTO I600 II. a I I OUTPUT CURRENT N 0) b (I G '4 (D D I O 1 I I l 0 IO TO I I0 I30 L l N E VOL r5 INVENTOR. JACK D. WELCH BY A 1 1 ORNE AGE T Iowa Filed May 19, 1958, Ser. No. 736,240 4 Claims. (Cl. 323-43) This invention relates generally to magnetic voltage regulation and more particularly to signal translating devices employing the saturation characteristics of magnetic cores as a regulating principle.

it is well known that the ampere-turns in the primary and secondary windings of a transformer are equal, as suming no losses and under conditions wherein the trans former core is not saturated. The present invention operates on the principle that the ampere-turns in the windings of a transformer must be maintained equal and the invention further incorporates the saturation effects of magnetic cores to provide a voltage reference device, the output of which is essentially Zero until a voltage source applied to the primary winding reaches a predetermined level, afterwhich time the output of the device increases linearly with input voltage.

The present invention is, therefore, termed a magnetic voltage reference and concerns a device which may be used to monitor an alternating current voltage source. The device of the present invention provides an output voltage characteristic which is essentially zero until the input reaches a preselected value and then rises linearly with further increase in input voltage. This particular characteristic might be particularly useful, for example, in a voltage monitoring system wherein a relay is desired to be closed at some particular line signal level and it is desirable that the relay shall close as the input level reaches a predetermined value and further shall release with decreasing input signal at a voltage level essentially that at which it was closed. It is well known that a relay which will close at 60 volts, for example, will not release until the voltage applied to its coil falls substantially below the 60 volt level. By the present invention, the linear increasing input signal characteristic may be converted to a more desired characteristic with a delay feature of sorts whereby the linear increasing signal may be made to be essentially zero until a predetermined input level is reached and may then assume a linear increasing characteristic having a steepness substantially greater than that of the input signal characteristic.

The device of the present invention is essentially a controlled transformer having a single primary winding wound about two cores with each of the cores having wound thereon a secondary winding. At least one of the cores is of the saturable type with a well-known square hysteresis characteristic. By proper choice of the load on this core, control of the ampere-turns in both secondary windings is maintained by the winding on the saturable core until such a time as the saturable core reaches the saturation point. The other secondary winding, through the range of input voltages below saturation of the saturable core is held to essentially a zero voltage level and begins to rise linearly at the saturation point of the saturable core.

it is an object therefore of the invention to provide a magnetic voltage reference device operating upon saturable core characteristics which converts a linear input signal into an output signal which is essentially zero until a predetermined input signal level is reached and which begins from this point to rise linearly at a predetermined rate for continued increase in input signal level. It is a further object of this invention to provide a magnetic voltage regulating device by which the output voltage 3,@3i,2h2 Patented May 22, 1932 characteristic may be readily governed by a preselected choice of turns ratios and secondary load values,

These and other objects and features of the invention will become more apparent from a reading of the following description in conjunction with the accompanying drawing, in which:

FIGURE 1 is a schematic representation of an embodiment of the invention;

FIGURE 2 is a representation of the ideal output voltage characteristics of the invention; and

FIGURE 3 is an actual output voltage characteristic of a circuit constructed according to the principles of this invention.

With reference to FIGURE 1, the invention is seen to be comprised of a pair of cores 15 and 16 upon which is wound a primary winding 11. Primary winding 11 is common to each of the cores 15 and 16. A secondary winding 12 is Wound about core 15 and a second secondary winding 13 is wound about core 16. A load resistor 24 is connected across secondary winding 13. A'load resistance 17 is connected to a center tap on secondary winding 12 and through two diodes 18 and 19 to the ends of secondary winding 12.. This latter arrangement provides a well-known full wave rectifier circuit as load on secondary winding 12. For the purpose of the operating principle of the present invention, how ever, the load may be considered as the resistor 17 across one-half of secondary winding 12. Core 16 is of the saturable type and thus primary winding 11 and secondary winding 13 operate as a saturable transformer with the core 16 possessing a square hysteresis characteristic such that the voltage induced in secondary winding 13 increases linearly with signal applied to primary winding 11 until a saturation point is reached, at which time it essentially levels ed at a predetermined voltage level.

Prior to saturation of core 16, the ampere-turns of secondary windings 12 and 13 each equal those of primary 11 according to well-known transformer characteristics and, therefore, are themselves equal. The load resistor 24 across secondary winding 13 is chosen as a relatively high resistance value such that the current in secondary winding 13 is held to a low value. This low value of current prior to saturation of core 16 determines the value of the ampere-turns which will exist in secondary winding 12 and the number of turns of secondary winding 12 may then be so chosen that an extremely small current will flow in the circuit of secondary winding 12 and this current in conjunction with the load resistance 17 on secondary winding 12 maintains an extremely low voltage drop across load resistance 17. Secondary winding 13 possesses a number of turns which in conjunction with its high load resistance 24 may be made to control the ampere-turn situation existing in all the windings prior to saturation. This control is efiective until the input signal level applied to primary winding 11 reaches a value such that core 16 saturates. For input signal levels beyond this saturation point, secondary winding 13 and core 16 no longer exercise their control. The output voltage across resistance 24 remains essentially constant and the ampereturn relationship existing in secondary winding 12 becomes independent of that of winding 13. The current in secondary winding 12 then increases in a normal linear fashion with increased primary signals such that the voltage across load resistor 17 increases linearly from its near zero value.

The ideal output characteristic of the device of FIG- URE 1 is shown in FIGURE 2, wherein the output voltage across load resistor 17 is plotted as line ABC. This output level is seen to be ideally zero for input voltages up to approximately volts and then increases linearly from point B to point C as the input voltage increases above the level at point B. The line AB'C is the ideal plot of the voltage across the controlling load resistor 24 on secondary winding 13. This characteristic is seen to increase linearly from point A to point B and then levels off in the portion shown from B to C. The point B represents in FIGURE 2 the value of input voltage (in this case approximately 95 volts) at which core 16 begins to saturate over a portion of each half cycle. It is noted that the two output voltage plots have essentially opposite characteristics for input voltage levels below the satura tion point B and for those levels above the saturation point B.

The manner in which these voltage characteristics are essentially attained may be then fully described by consideration of actual voltage values, turns ratio and load resistance values. For example, consider it desirable to construct a device to monitor a 400 cycle per second power line voltage where the output from the monitoring device is to remain essentially at zero until the supply voltage reaches 95 volts. It is desirable that, for supply voltages above 95 volts, the output should increase linearly for input up to at least 135 volts where the output should deliver 20 milliamperes into a 1,750 ohm load. For this application, the primary winding 11 contains 1,900 turns and secondary winding 12 is provided with a center tapped winding of 3,800 turns, while secondary winding 13 is provided with 1,125 turns across which is connected a relatively high resistance of 560,000 ohms. As previously discussed, prior to saturation of core 16, the ampere-turns in both secondaries are equal. Since secondary winding 13 on saturable core 16 is operating into a relatively high resistance load 24, the current in secondary winding 13 is low. The manner in which the load resistance 24 may be made to control the ampere-turns situation might be further considered upon the basis of the relative manner in which load resistance 17 and 2 4 are reflected back into the primary winding 11. In the example under consideration, the 560,000 ohm resistor 24 reflects into the primary, due to the coupling ratio as well over a million ohms, whereas the 1,750 ohm resistor 17 through its one-to-one coupling ratio reflects back in as but 1,750 ohms. It is thus seen that prior to any saturation eifects, the current flowing in the primary winding 11 is essentially governed by load resistor 24. This control is exercised until core 16 saturates, at which time load resistor 24 is not effectively coupled into the primary circuit and actually the load resistance 24 in conjunction with secondary winding 13 on core 16 exercises no further control over the primary current. For example, the resistance reflected in primary winding 11 is, from its turns ratio with respect to secondary windings 12 and 13, approximately 1,565,000 ohms. Thus as the 400 cycle supply voltage reaches 95 volts, approximately 0.06 milliampere flows in primary winding 11.

Since equal ampere-turns must exist in secondary winding 12, it is seen that, in conjunction with the 1,900 turns of each half of winding 12, the same current or approximately .06 milliampere will flow through the 1,750 ohm resistor 17, which results in a voltage across resistor 17 of approximately i volt. From the turns ratio between primary 11 and secondary 13, approximately 0.1 milliampere flows in secondary 13 and approximately 56.2 volts is developed across resistor 24. This particular 95 volt input level is discussed since in this case it is the level which, in conjunction with core 16, secondary winding 13, and load resistance 24, determines the saturation point of core 16. Thus in FIGURE 2, the saturation point is indicated at B and B on the output curves. The output voltage at point B across resistance 24 is illustrated as being 56 volts, while the output voltage at point B across resistor 17 is shown to be ideally zero and as indicated above is in the neighborhood of of a volt as compared to the 5 6 volts across secondary winding 13-. As the input voltage increases above 95 volts, core 16 saturates over a greater and greater portion of the cycle until with 135 volts input approximately 40 vol-ts appears across load resistor 17.

A regulating device constructed according to this invention and having parameters as discussed above provided the output characteristic illustrated in FIGURE 3. It is seen that the characteristic is essentially zero for line voltage values up to approximately volts, at which time it begins to increase linearly with line voltage in-i crease. The actual characteristic in FIGURE 3 is thus seen to approximate the ideal characteristic ABC of FIGURE 2. It is realized that the zero level of the output characteristic is not attained in practice since the zero level is based on ideal transformer characteristics wherein inherent losses have been neglected, and assumes infinite resistance being reflected into primary 11 by resistor 24 across secondary 13.

As previously discussed, the output characteristic ABC of FIGURE 2 might be valuable for a monitoring system which employs a relay. With reference to FIGURE 2, a dotted linear characteristic AD is illustrated which might be, for example, any linearly increasing line voltage. If a relay were to be energized with this voltage characteristic applied to its coil, the relay might close, for example, as the input voltage reached approximately volts or point D on the dotted characteristic. Now as the input voltage decreases along the line DA, the relay, due to inherent characteristics, might not release until the point B were reached or at approximately 60 volts, for example. It is seen that by utilizing the device of the present invention the line voltage characteristic may be converted to the line ABC by projecting the point E to point E on characteristic ABC. It is seen that the same relay might be made to energize as point D is reached and deenergized at point E. The variation in input voltage at the energizing and release points for the same relay is thus seen to be considerably narrowed.

It is seen that by the present invention a magnetic voltage reference device is provided by which a linearly increasing alternating current signal may be converted to a signal which is essentially zero until a predetermined input level is reached and thereafter increases proportionally with input signal.

Although this invention has been described with respect to a particular embodiment thereof, it is not to be so limited as changes and modifications may be made therein which are within the full intended scope of the invention as defined by the appended claims.

I claim:

1. A magnetic voltage translating device comprising first and second cores having a common primary winding thereon and first and second secondary windings wound individually on each of said cores, an input signal applied to said primary winding, said first secondary winding connected to an output resistance load and having a predetermined number of turns so as to reflect comparatively small resistance into said primary winding, said second secondary winding having a predetermined number of turns and connected to a resistance load so as to reflect a considerably greater resistance into the said primary winding so as to essentially determine the current in said primary winding, said second core being saturable at a predetermined level of said input signal, said first core being unsaturable over the variable range of said input signal whereby for values of said input signal below the predetermined level at which said second core begins to saturate the ampere-turns in said first secondary winding are essentially equal to those in said second secondary winding and the current in said first secondary winding is held to a low level, and above the saturation point of said second core the current in said first secondary winding increases linearly with said input signal.

2. A magnetic voltage translating device comprising first and second magnetic cores upon which is Wound a primary winding common to both of said cores and first and second secondary windings wound individually on said a) first and second cores respectively, an input signal applied to said primary winding, said input signal being variable in magnitude over a predetermined range, a resistance connected across each of said secondary windings, the turns ratios between said primary winding and said first and second secondary windings being predetermined such that the load across said second secondary winding refiects into said primary winding at an effective value substantially greater than that reflected thereinto by the load across said first secondary winding and the current flow in said primary winding is held at a low value thereby holding the current in said first secondary winding to a low value in accordance with its ampere-turns relationship with said primary and said second secondary windings, said first core being unsaturable over the predetermined range of said input signal, said second co-re being saturable at a predetermined magnitude within the predetermined range of variation of said input signal, whereby the voltage developed across said second secondary resistance increases proportionally with primary voltage and the voltage across said first secondary winding is held at a low value for input voltage levels below the saturation point of said second core and the voltage across said first secondary resistance varies linearly with input voltage for input signal levels exceeding the saturation point of said second core.

3. A magnetic voltage translating device comprising first and second magnetic cores, a primary Winding wound common to each of said cores and first and second secondary windings wound individually about said first and second cores, each of said secondary windings connected to a resistance load, the resistance across the second secondary winding being substantially greater than the resistance across said first secondary winding and thereby substantially determining the current flo-w in said primary winding, an input signal applied to said primary winding, said input signal being variable in magnitude over a predetermined range, said second core being saturable at a predetermined level of said input signal, said first core being unsaturable over the range of said input signal, the first secondary winding having a number of turns such that the current in said windings is held to a low value for magnitudes of input signal below the predetermined level thereof suffieient to saturate said second core, the current in said first secondary winding increasing linearly with increase of primary signal voltage above the saturation point of said second core.

4. A magnetic voltage translating device comprising first and second cores said second core being of the saturable square hysteresis type, a primary winding wound common to each of said first and second cores, a first secondary winding wound on said first core, a second secondary winding wound on said second core, each of said secondary windings connected to a load resistance, the load resistance for said second secondary winding being substantially greater than that for said first secondary winding, whereby the ampere-turns in said first secondary winding are controlled by those present in said second secondary winding, an input signal applied to said primary winding, said input signal being variable over a predetermined range Within which a predetermined level is sufiicient to saturate said second core and throughout which said first core is unsaturable whereby the current in said first secondary winding is held to a substantially constant low value below the saturation level of said second core and increases linearly with input signal levels above said saturation level.

References Cited in the file of this patent UNITED STATES PATENTS 2,809,302 Lawrence Oct. 8, 1957 FOREIGN PATENTS 295,500 Switzerland Mar. 1, 1954 472,521 Great Britain Sept. 24, 1937 

